I just upgraded from 4.0 to 5.0 TMS. Some of my videos play some do not. The ones that do claim to be "Microsoft ASF" according to a linux "file" command. I've tried avi, mp4 and h264, none of which the 360 will play. I'm converting with Handbrake on a Mac laptop. I did install the codec upgrade last night.

I'm in the same boat. I installed twonky server on ubuntu jaunty. The only format I've been able to stream so far is a windows media format. Is there on the fly transcoding cause not even avi's are working and xbox put out a patch for those.

Just in case anyone else is having this - I think the problem is the xbox360's limited playback codecs. Out of the box it works with .WMV and if you have a live connection you can download the Divx codec. It will still have problems playing certain Xvid files.